Abrasive tool insert

Abstract: An abrasive tool insert (10) comprises a cemented metallic substrate (11) and a polycrystalline diamond layer (12) formed thereon by high pressure, high temperature processing. The interface between the substrate and the diamond layer forms a sawtooth shaped cross-sectional profile (13,15) including a number of surfaces (14) sloping outwardly and downwardly toward a cutting edge (25) of the insert.

Description: Field of the Invention The present invention relates to the field of abrasive tool inserts and, more particularly, to such inserts having a sawtooth shaped diamond/substrate interface to provide improved durability and reduced susceptibility to spalling, cracking and wear of the diamond layer. Background of the Invention Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. The abrasive compacts typically consist of polycrystalline diamond or cubic boron nitride particles bonded into a coherent hard conglomerate. The abrasive particle content of abrasive compacts is high and there is an extensive amount of direct particle-to-particle bonding. Abrasive compacts are made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable. Abrasive compacts tend to be brittle and, in use, they are frequently supported by being bonded to a cemented carbide substrate. Such supported abrasive compacts are known in the art as composite abrasive compacts. The composite abrasive compact may be used as such in the working surface of an abrasive tool. Alternatively, particularly in drilling and mining operations, it has been found advantageous to bond the composite abrasive compact to an elongated cemented carbide pin to produce what is known as a stud cutter. The stud cutter is then mounted in the working surface of a drill bit or a mining pick. Fabrication of the composite is typically achieved by placing a cemented carbide substrate into the container of a press. A mixture of diamond grains or diamond grains and catalyst binder is placed atop the substrate and compressed under high pressure, high temperature (HPHT) conditions. In so doing, metal binder migrates from the substrate and "sweeps" through the diamond grains to promote a sintering of the diamond grains. As a result, the diamond grains become bonded to each other to form a diamond layer, and that diamond layer is bonded to the substrate along a conventionally planar interface. Metal binder remains disposed in the diamond layer within pores defined between the diamond grains. A composite formed in the above-described manner may be subject to a number of shortcomings. For example, the coefficients of thermal expansion and elastic constants of cemented carbide and diamond are close but not exactly the same. Thus, during heating or cooling of the polycrystalline diamond compact (PDC), thermally induced stresses occur at the interface between the diamond layer and the cemented carbide substrate, the magnitude of these stresses being dependent on the disparity in thermal expansion coefficients and elastic constants. Another potential shortcoming which should be considered relates to the creation of internal stresses within the diamond layer which can result in a fracturing of that layer. Such stresses also result from the presence of the cemented carbide substrate and are distributed according to the size, geometry and physical properties of the cemented carbide substrate and the polycrystalline diamond layer. European Patent Application No. 0133 386 suggests a PDC in which the polycrystalline diamond body is completely free of metal binders and is to be mounted directly on a metal support. However, the mounting of a diamond body directly on metal presents significant problems relating to the inability of the metal to provide sufficient support for the diamond body. The European Patent Application further suggests the use of spaced ribs on the bottom surface of the diamond layer which are to be embedded in the metal support. According to the European Patent Application, the irregularities can be formed in the diamond body after the diamond body has been formed, e.g. , by laser or electronic discharge treatment, or during the formation of the diamond body in a press, e.g. , by the use of a mold having irregularities. As regards the latter, it is further suggested that a suitable mold could be formed of cemented carbide; in such case, however, metal binder would migrate from the mold and into the diamond body, contrary to the stated goal of providing a metal free diamond layer. The reference proposes to mitigate this problem by immersing the thus-formed diamond/carbide composite in an acid bath which would dissolve the carbide mold and leach all metal binder from the diamond body. There would thus result a diamond body containing no metal binder and which would be mounted directly on a metal support. Notwithstanding any advantages which may result from such a structure, significant disadvantages still remain, as explained below. In sum, the European Patent Application proposes to eliminate the problems associated with the presence of a cemented carbide substrate and the presence of metal binder in the diamond layer by completely eliminating the cemented carbide substrate and the metal binder. However, even though the absence of metal binder renders the diamond layer more thermally stable, it also renders the diamond layer less impact resistant. That is, the diamond layer is more likely to be chipped by hard impacts, a characteristic which presents serious problems during the drilling of hard substances such as rock. It will also be appreciated that the direct mounting of a diamond body on a metal support will not, in itself, alleviate the previously noted problem involving the creation of stresses at the interface between the diamond and metal, which problem results from the very large disparity in the coefficients of thermal expansion between diamond and metal. For example, the thermal expansion coefficient of diamond is about 45x10 -7 cm/cm/°C as compared to a coefficient of 150-200x10 -7 cm/cm/°C for steel. Thus, very substantial thermally induced stresses will occur at the interface. In addition, once the portions of the diamond which do not carry the ribs begin to wear sufficiently to expose the metal therebehind, that metal will wear rapidly, due to its relative ductility and lower abrasion/erosion resistance, and undermine the integrity of the bond between the diamond and the metal support. Recently, various PDC structures have been proposed in which the diamond/carbide interface contains a number of ridges, grooves or other indentations aimed at reducing the susceptibility of the diamond/carbide interface to mechanical and thermal stresses. In U.S. Patent No. 4,784,023, a PDC includes an interface having a number of alternating grooves and ridges, the top and bottom of which are substantially parallel with the compact surface and the sides of which are substantially perpendicular the compact surface. U.S. Patent No. 4,972,637 provides a PDC having an interface containing discrete, spaced recesses extending into the cemented carbide layer, the recesses containing abrasive material ( e.g., diamond) and being arranged in a series of rows, each recess being staggered relative to its nearest neighbor in an adjacent row. It is asserted in the '637 patent that as wear reaches the diamond/carbide interface, the recesses, filled with diamond, wear less rapidly than the cemented carbide and act, in effect, as cutting ridges or projections. When the PDC is mounted on a stud cutter, as shown in Fig. 5 of the '637 patent, the wear plane 38 exposes carbide regions 42 which wear much more rapidly than the diamond material in the recesses 18. As a consequence, depressions develop in these regions between the diamond filled recesses. The '637 patent asserts that these depressed regions, which expose additional edges of diamond material, enhance the cutting action of the PDC. U.S. Patent No. 5,007,207 presents an alternative PDC structure having a number of recesses in the carbide layer, each filled with diamond, which make up a spiral or concentric circular pattern, looking down at the disc shaped compact. Thus, the '207 structure differs from the '637 structure in that, rather than employing a large number of discrete recesses, the '207 structure uses one or a few elongated recesses which make up a spiral or concentric circular pattern. Fig. 5 in the '207 patent shows the wear plane which develops when the PDC is mounted and used on a stud cutter. As with the'637 patent, the wear process creates depressions in the carbide material between the diamond filled recesses. Like the '207 patent, the '637 patent also asserts that these depressions which develop during the wear process enhance cutting action. U.S Patent No 5,011,515, which represents the closest prior art document, presents a further PDC structure in which the interface between the abrasive layer and the substrate has various forms, particularly corrugated structures. Whereas the aforementioned patents assert a desirable cutting action in the rock, it is also highly desirable to minimize the diamond layer's susceptibility to fracture and spalling which in part arises from the internal residual stresses. Accordingly, it would be highly desirable to provide a polycrystalline diamond compact having increased resistance to diamond spalling fractures. Summary of the Invention According to the invention, there is provided a tool insert, comprising: a substrate; a continuous abrasive layer having a periphery forming a cutting surface, said abrasive layer being integrally formed on said substrate and defining an interface therebetween, wherein said interface includes a plurality of sloped regions, characterised in that said interface has a sawtooth shaped contour in cross section with a sloped region with a surface extending from said cutting surface such that said abrasive layer is thicker at said cutting surface than at regions immediately and radially interior to said cutting surface. Thus, embodiments of the invention can provide a polycrystalline compact having increased useful life. Furthermore, the invention can provide a PDC in which polycrystalline diamond compact having a diamond layer formed such that there is reduced spalling and cracking of the diamond layer as the compact wears. Still further the invention can provide a PDC in the carbide layer which provides increased mechanical support for the diamond layer as the compact wears. The diamond-carbide interface plane may substantially intersect the cutting edge at an angle, said angle being about 20-50 degrees With the wear plane which develops during use. The improved polycrystalline diamond compact may have at least one angled contour in the carbide layer, said layer being covered with diamond or other abrasive material shaped such that it provides an outwardly sloping profile at the cutting edge of the compact. The angle of the outwardly sloping profile can be matched to the anticipated angle of the wear plane which will develop as the PDC wears. Further, the carbide substrate may include more than one contour or a repeating pattern of contours. Advantageously, the profile of repeating contours will form a sawtooth like pattern when projected onto a plane perpendicular to the anticipated wear plane. Accordingly, a PDC having a sawtooth like pattern of contours sloping outwardly toward the cutting edge can be formed from a single spiral shaped contour, multiple concentric contours, multiple concentric contours with gaps, or a series of straight or otherwise shaped contours. Brief Description of the Drawings The invention will now be described in greater detail, by way of example, with reference to the drawings in which: FIG. 1 depicts a cross-sectional view of a PDC having a repeating, outwardly sloping pattern in accordance with the invention; FIG. 2 depicts a top view of a PDC having a concentric pattern of outwardly sloping contours in accordance with the invention; FIG. 3 depicts a top view of a PDC having a concentric pattern, with gaps, of outwardly sloping contours in accordance with the invention; and, FIG. 4 depicts a top view of a PDC having a repeating linear pattern of outwardly sloping contours in accordance with the present invention. Detailed Description of the Invention Reference is now made to FIG. 1 which shows an exemplary cross-sectional profile of a PDC in accordance with the invention. PDC 10 includes a substrate 11, preferably comprised of cemented carbide, and an abrasive layer 12, preferably comprised of polycrystalline diamond. Abrasive layer 12 is integrally bonded to substrate 11 and, in the typical manufacturing process, will be formed thereon by HPHT processing. For reference, FIG. 1 depicts the cutting edge 25 and anticipated wear plane 16 of PDC 10. In application, edge 25 and plane 16 will, of course, depend on the manner in which PDC 10 is mounted on a stud cutter or other support means. As illustratively depicted in FIG. 1, the cross sectional profile of the boundary between substrate 11 and abrasive layer 12 comprises a plurality of contoured surfaces, each having a bottom notch 13 and a top ridge 15 associated therewith. Further associated with each contour is an outwardly sloping surface 14. Surface 14 slopes outwardly and downwardiy toward cutting edge 25 and is preferably angled so that said angle is about 20-50 degrees with the anticipated wear plane 16. In use, as PDC 10 wears, wear plane 16 (which represents the surface providing cutting action) slowly descends. Until wear plane 16 reaches the first sloping surface 14, wear plane 16 intersects only the abrasive layer 12, which provides excellent cutting and wear characteristics. Compared to abrasive layer 12, substrate layer 11 wears relatively quickly. Therefore, once wear plane 16 descends beyond the first sloping surface 14, the substrate material 11 intersecting wear plane 16 erodes away more quickly and a diamond lip forms according to accepted understanding to those knowledgeable of typical PDC wear characteristics. During drilling, PDC 10 experiences very high stresses in the abrasive, or diamond, layer 12, particularly near the interface with substrate 11. Such stresses, some of which have been previously discussed, lead to fracturing and spalling in the diamond layer. These application stresses occur randomly and intermittently during drilling. They vary in magnitude and direction according to the localized contact dynamics with the rock face and rock particles in the hole. During events characterized by high tensile stress, cracks can form in the diamond layer. These cracks, being subjected to repeated high stress events, can propagate to form fracturing and spalling of the diamond layer. One region particularly susceptible to such occurrence is at or very near the diamond-carbide interface in the diamond layer. This region, in PDC's not of the present invention, suffers from pre-existing high residual tensile stresses which have previously been discussed. Advantageously, the cross-sectional profile depicted in FIG. 1 reduces the axial residual tensile stresses in the diamond or abrasive layer 11 at the wear or contact surfaces of the diamond or abrasive layer 11, thereby reducing spalling and premature wear in the abrasive layer 12. There are many ways in which the sawtooth shaped cross-sectional profile depicted in FIG. 1 can be implemented in an industry compatible disc shaped abrasive compact. FIGS. 2-4 present top views of three such exemplary embodiments. FIG. 2 shows a PDC 10a wherein the top ridges 15 of the contours form a concentric circular pattern. Outwardly and downwardly sloping surfaces (not visible) angle radially toward cutting surface 25. A radially cut cross-section of PDC 10a would show the characteristic sawtooth shaped profile of the interface. FIG. 3 shows a similar PDC 10b in which the ridges 15 form a concentric circular pattern with gaps. FIG. 4 depicts a PDC 10c having a linear pattern of contours. The abrasive/substrate interface of PDC 10c includes a plurality of surfaces sloping from the top ridges 15 outwardly toward cutting surface 25. A vertically cut cross-section of PDC 10c would reveal the sawtooth shaped profile of FIG. 1. Other embodiments, such as one based on a spirally shaped pattern of recesses, are also possible. While the invention has been described with reference to the presently preferred embodiments thereof, it is understood that the scope of the invention shall be limited only in accordance with the following claims.

Claims: A tool insert (10), comprising: a substrate (11); a continuous abrasive layer (12) having a periphery forming a cutting surface (25), said abrasive layer (12) being integrally formed on said substrate (11) and defining an interface therebetween which includes a plurality of sloped regions, characterised in that said interface has a sawtooth shaped contour in cross section with a sloped region (14) with a surface extending from said cutting surface such that said abrasive layer is thicker at said cutting surface than at regions immediately and radially interior to said cutting surface. A tool insert as defined in claim 1 wherein the plurality of sloped regions forms a concentric circular pattern about a central axis of the insert. A tool insert as defined in claim 1, wherein said interface has a plurality of sloped regions forming a repeating linear pattern. An abrasive tool insert as defined in claim 1, 2 or 3 wherein said substrate (11) is made of cemented carbide. An abrasive tool insert as defined in any of claims 1 to 4 wherein said abrasive layer (12) is made of polycrystalline diamond. A tool insert as defined in any preceding claim wherein the slope of said plurality of sloped regions is selected from an angle between about 20 and 50 degrees to an anticipated wear plane.

Inventors: FLOOD GARY MARTIN, JOHNSON DAVID MARK, FLOOD, GARY MARTIN, JOHNSON, DAVID MARK
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1994
Main classification: B23B27
IPC codes: E21B10, B24D3, B23B27, B24D99